WASHINGTON (November 10, 1999 6:02 p.m. EST http://www.nandotimes.com)
- For nine months, the Mars Climate Orbiter was speeding through space
and speaking to NASA in metrics. But the engineers on the ground were replying
in non-metric English.

The mathematical mismatch that was not caught until after the $125 million
spacecraft, a key part of NASA's Mars exploration program, was sent crashing
too low and too fast into the Martian atmosphere. The craft has not been
heard from since.

"We were on the wrong trajectory and our system of checks and balances
did not allow us to recognize that," Edward Stone, director of the
Jet Propulsion Laboratory, said Wednesday. The NASA center in California
was in charge of the Mars mission.

Noel Henners of Lockheed Martin Astronautics, the prime contractor for
the Mars craft, said at a news conference that his company's engineers
were responsible for ensuring that the metric data used in one computer
program were compatible with the English measures used by another program.
The simple conversion check was not done, he said.

Art Stephenson, director of the Marshall Spaceflight Center and head
of a NASA investigation team, said that the spacecraft was not symmetrical
and that pressure from the sun caused it to slowly twist or roll as it
sped along. On-board gyroscopes partially controlled the motion, but eventually
rocket firings were needed to stabilize the craft, he said. This happened
12 to 14 times a week over the nine-month voyage.

Engineers on the ground calculated the size of the rocket firing using
feet-per-second of thrust, a value based on the English measure of feet
and inches. However, the spacecraft computer interpreted the instructions
in Newtons-per-second, a metric measure of thrust. The difference is 4.4
feet per second.

"Each time there was a burn (rocket firing) the error built up,"
said Stephenson.

As the spacecraft approached its rendezvous with Mars and the engineers
prepared for a final rocket firing, there were indications that something
was seriously wrong with the navigation, but no corrective action was taken,
Stephenson said.

When the Mars Climate Orbiter did fire its rockets, the craft went too
low into the planet's atmosphere instead of into a safe orbit. Communication
signals stopped when the craft passed behind Mars and have not been heard
since.

"We entered the Mars atmosphere at a much lower altitude (than
planned)," said Ed Weiler, NASA's chief scientist. "It (the spacecraft)
either burned up in the Martian atmosphere or sped out (into space). We're
not sure which happened."

Stephenson said that the problem was not with the spacecraft, but with
the engineers and the systems used to direct it.

"The spacecraft did everything we asked of it," said Stephenson.
He said the mathematical mismatch was "a little thing" that could
have been easily fixed if it had been detected.

"Sometimes the little things can come back and really make a difference,"
he said.

Stone said that problems found in the Mars Climate Orbiter loss have
led to major changes in control and operation of a sister spacecraft, the
Mars Polar Lander, that is scheduled to land on Mars on Dec. 3.

"There were hard lessons to learn from the loss of the Mars Orbiter,
but learn them we will," said Stone. "We must learn and learn
quickly" because the Mars landing is just over three weeks away, he
said.

Following recommendations from Stephenson's investigation board, Stone
said the team directing the Mars Polar Lander has been reorganized and
strengthened. He said senior engineers have been added to the group and
a new system of review and evaluation has been installed. He said that
navigation of the Mars craft now will be checked by two independent means
to make sure it is on target for the landing.

Loss of the Mars Climate Orbiter is a serious blow to NASA's exploration
program. The spacecraft was to orbit Mars and act as a radio relay for
signals from the Mars lander. Those signals now will be routed through
another spacecraft.